Apparatus for use in measuring surface tension



Filed Sept. 16, 1950 mp m a mwy m .E. r. 1 "m H 2 b M 0 W/ Oct. 6, 1953 N. B. COLTH UP EIAL APPARATUS FOR USE IN MEASURING SURFACE TENSION Patented Oct. 6, 1 953 APPARATUS FOR USE IN MEASURING SURFACE TENSION Norman B. Colthup, Stamford, and Robert E.

Torley, Greenwich, Conn., assignors to American Cyanamid Company, New York, N. Y., a

corporation of Maine Application September 16, 1950, Serial No. 185,284

3 Claims. 1

This invention relates to an improved surface tension measuring device for liquids.

Surface tension of liquids has been measured by what is called the bubble method, in which the pressure required to form and burst a bubble of the liquid is measured. These devices require removal of excess liquid as they are very sensitive to the depth of liquid over the orifice.

Another serious drawback to the type of device where a single bubble is blown and burst is that only one Or at most a very limited number of measurements can be made without opening up the equipment and adding more liquid. It has also been proposed to force gas through a manometer tube. This however, has required that the level of the liquid in the manometer tube legs be kept at an accurately, predicted point.

While it has been possible with some of the bubble instruments used in the past, and referred to above, to make fairly accurate measurements of surface tension when great caution was exercised, they have been much less satisfactory in the hands of the ordinary laboratory technician and for the most part these devices have made a large number of measurements in quick succession difficult or impossible. Averaging of readings has therefore been practically out of the question and the increased reliability and accuracy obtainable by averaging a number of readings is still something which could not be practically obtained on the instruments hitherto designed.

Another drawback has been the price and complexity of the apparatus and the practical impossibility of making measurements on a number of liquids in a short time because the apparatus used hitherto did not permit rapid disassembly and cleaning.

The present invention is directed to a very simple, cheap and reliable instrument which permits multiple readings in rapid succession and can be used to measure the surface tension of a number of liquids in fairly rapid succession. The typical embodiment of the invention lies in the drawings:

Fig. 1 is an elevation of the device.

Fig. 2 is a longitudinal section, slightly enlarged, along the line 22 of Fig. 1.

Figure 3 is an elevation of the device, partly reken away, showing a further modification of the scale illustrated in connection with the device shown in Figure 1.

The device comprises an elongated glass vessel 1, provided with an enlarged bulb 2. In the vessel there projects an open-end measuring tube 3, provided with an accurately calibrated fine orifice i, and connected through the pipe I, 'to a source of gas under pressure, for example,

an ordinary laboratory compressed air pipe. A scale 3a is mounted adjacent'to the container l and is adjustably and detachably secured there- "to as shown in Figure 3, or if desired the scale may be etched thereon'as shown in Figure 1.

In operation, the container l is filled with the liquid, the surface tension of which is to be measured, until the latter partly fills the bulb 2 and submerges the orifice 4. Pressure on the gas is then increased until bubbles 6 start to escape from the orifice 4. The pressure at the moment of escape is measured by the depression of the meniscus 5, below the orifice 4, in the control tube 3. The scales 8 and 8a may be suitably calibrated so that the meniscus position gives a measure of the desired surface tension. A microscope or' magnifying reading glasses (not shown) may be provided to read the scale more accurately, as is conventional in measuring instruments. The equation giving the measurement of surface tension is as follows:

where X is the displacement of the meniscus below the orifice when bubbling occurs, g the gravity constant, p the liquid density, d the diameter of the orifice; and v the surface tension. In operation the pressure is slowly increased until bubbling starts, at which point the meniscus will rise until bubbling ceases, and the cycle is repeated. Preferably, the flow of gas under pressure is arranged to lower the meniscus about 2 or 3 mm. per second. A number of readings may be taken in quick succession of all the lowest points reached by the meniscus, that is to say, at the instant bubbling starts, and the average may be taken for greater accuracy.

One of the marked advantages of the present invention is that within wide limits the height of the liquid in the bulb or tube above the orifice even 10 cm. of water, requires only a second order correction in the result. It is therefore not necessary to fill the device to an exact level and the accuracy of the measurement does not depend on great care in operation. On the other hand, accuracy is affected by the size of the orifice and by the requirement that the material surrounding the orifice be uniformly wet by the liquid. For this reason it is desirable to use a material that is readily wet, for example, a

small platinum disc sealed into the central glass substance x mre ctayfiesm di s/anti Carbon tetrachloride... 4. 19 25.0 25. 89 26. 0 Acetone 7. 42 25, O. 22.77. 23, 0 Benzene 8. 27 damn i 28$ 1! $8. 1-

When it is desired to measure a number of different. liquids,v it is only necessary to change the inner tube 3 with its orifice. This can be transferred from. one container containing one liquid. to alnothencoz'itain'er containing another liquid with rapid cleaning between measuremerits, an advanta e not possessed by instrumefitszfii'therto. usemgwner'e meaning" or: the whole instrument was necessar when changing from one" liquid. to another; fep'r'es'entihg, a fairly" time consuming" operation.

Antither ver i'riifibft'aint advantage of the present invention for; certam. specialized uses is that its operati n; depends on a pressure difierential between the, gas pressure' the inner tube and. the pressure at the Orifice. In. most? cases. the pressure on the liquid inthe' open-end cont'ainer is afirh'dsrihfiol however; this" is not at all' necessar for" the opu'atibu of the device arid the liquid iii the". o en-end. c'ont'a'mer' may be under pressure ahove' of he1ow'tli'e atmosphere'. This makes it possible for" the first time to measure practically surface tension changes systerr'rswhich are under pressure opening. a

new field for urface. tfisio'h measurements. In

We claimf 1. An apparatus for use in measuring the surface tension of a liquid comprisin an elongated, close-end liquid container, a concentric open-ended inner tube extending nearly to the bottom (it said contaii'ri'eh. said. outer container and said ihner tube lacing of transparent material, said inner tube having an orifice in the side thereof below the normal level to which liquid fill-ed into said outer container, an adjustable scale mounted adjacent to the lower end of said container, and means for applying iricreas'ihg" pressure of gas to said inner tube wiierefigthef depression of the meniscus below the. dfifice; of said inner tube may be read on aim scale at the moment bubbles emerge from semi orifice:

2. A device according to claim 1 in which the outer" container is provided with an enlarged section at the upper end thereof.

3 apparatus for use measuring the surface tensionof a liquid com rising an aidegated transparent tube closed at one end; an inner transparent tubeopen at both ends vertically disposed wit-hirisaid outer tube and extending downwardly adjacent to the bottom thereof, said inner tube having" an orifice in the wall thereof located below the norm'aT liquid level in said outer tube; means for supplying gas under pressure tosaid i'nne'r' tube sh as to" depress; the meniscus therein; and means for measusing the displacement of' the meniscus from theorifice of said inner tube.

NORA/LANE. coL rrruP. ROBERT E; T'ORLEY.

R'tllitefences Gite'd the" file of this 15213611 11 UNITED STATES PATENTS 

